Revieivs — Geology of Windsor and Chertsey. 233 



and also at Windsor Castle. In the old series of Geological Survey- 

 maps the Windsor Chalk is shown as part of the main mass of Chalk 

 of the Chiltern Hills, but, as was suggested some time ago by 

 Mr. Whitaker, it is now proved to be a small inlier due to a post-Eocene 

 anticline. This is explained by the authors in a most interesting 

 horizontal section (p. 13), which shows how the Chalk of the Castle 

 Hill projects through the Eocene formations. 



The second or southern third of the district is occupied by what 

 used to be known as the Bagshot Sands. There has been some 

 discussion as to whether they rest, conformably or unconformably, on 

 the London Clay, and the authors find that in part of the district the 

 junction is conformable with passage beds, whilst in the western part 

 there is an abrupt change of sedimentation with indications of erosion 

 of the London Clay before the Bagshot Sands were deposited The 

 Bagshot Sands were divided by Prestwich in 1847 into three 

 divisions, all of which can be more or less satisfactorily correlated with 

 beds in the Hampshire Basin. The question thus arises whether to 

 use the London Basin or the Hampshire Basin names, and the authors 

 of the present work have decided to restrict the name Bagshot to the 

 lowest of the three divisions, and to use the Hampshire names 

 Bracklesham and Barton for the middle and upper divisions 

 respectively, (p. 32.) 



The Bagshot Beds are mainly current-bedded sands with thin layers 

 of clay and pipe-clay and occasionally beds of pebbles. The thickness 

 does not exceed 120 feet, and they thin to 20 feet towards the north. 

 There are practically no fossils. 



The Bracklesham Beds contain clay suitable for brick-making and 

 beds of green sand. Fossils have been found which satisfactorily 

 prove their Bracklesham age. The thickness is estimated at 100 feet 

 at St. George's Hill, near Weybridge, and in the west of the district 

 the thickness maybe as much as 80 feet, but is very variable, (p. 42.) 

 Pebble beds occur in places. Ironstone, an impure carbonate of iron, 

 is found at the junction of the Bracklesham and Bagshot Beds, and 

 was dug for smelting round St. George's Hill in the eighteenth and 

 beginning of the nineteenth centuries. It is remarked that no other 

 Tertiary iron-ore has been worked in the Thames Basin, though ore of 

 about the same age was formerly worked at Hengistbury Head on the 

 Hampshire coastt (p. 92.) 



The Barton Beds consist of light-coloured quartzose sand with 

 occasional beds of loam and clay and more rarely seams of pebbles. 

 Bedding is seldom seen and current-bedding, so common in the 

 Bagshot Beds, is exceptional in this upper series. The colour is 

 usually yellow or buff. Very few fossils have been found in this 

 district. * This is the topmost Eocene bed in the area, and the full 

 thickness is not preserved. The present- thickness may slightly 

 exceed 100 feet at Caesar's Camp, Easthampstead. Grey wethers or 

 sarsen stones have been found in considerable abundance in the 

 district, and though not seen in situ in Barton Beds, the authors think 

 it probable that they may have been formed in them. 



Much of the surface of this southern third of the district is covered 

 by Plateau Gravel, and the authors remark that " Presuming that the 



